1. Field of the Invention
This invention is in the field of railroad track switching equipment used to enable railroad vehicle traffic to pass along one or the other of two sets of tracks, at a point where the two sets of tracks merge into one set of tracks or where one set of tracks diverges into two sets of tracks, specifically equipment used to monitor the position of switching equipment at the merge/diverge point.
2. Background Art
In directing railroad vehicle traffic between one set of tracks and two sets of diverging tracks, with vehicles moving in either direction, it is well known to shift a set of point rails transversely, to cause one or the other of the point rails to contact a stationary stock rail. When viewed from the perspective of the single set of tracks, if the right hand point rail aligns with the right hand stock rail, traffic will be directed from the single set of tracks onto the left set of diverging tracks, or traffic coming from the left set of diverging tracks can pass onto the single set of tracks. Conversely, if the left hand point rail aligns with the left hand stock rail, traffic will be directed from the single set of tracks onto the right set of diverging tracks, or traffic coming from the right set of diverging tracks can pass onto the single set of tracks.
With this common type of switching arrangement, if the right hand point rail is aligned with the right hand stock rail, and if a rail vehicle passes from the right hand set of diverging tracks onto the single set of tracks, the right hand point rail will be forced away from the right hand stock rail. In this situation, commonly called a trailed switch condition, the right hand point rail may simply deflect and then return almost to its original alignment with the right hand stock rail, but remain somewhat separated from the right hand stock rail. This results in a condition which could lead to derailment when the next rail vehicle moving along the single set of tracks passes through the switch point, since neither the right hand point rail nor the left hand point rail aligns with its respective stock rail. In other words, the right wheel of the rail vehicle will attempt to follow the right hand set of diverging tracks, while the left wheel of the rail vehicle will attempt to follow the left hand set of diverging tracks. Even if the point rail rebounds to its original position in contact with the stock rail, the switch machine which holds the point rails in position may have been damaged and rendered incapable of adequately holding the point rail in position against the stock rail. This can still result in the derailing of a rail vehicle passing through the switch. It is necessary, therefore, to send an operator to a trailed switch, to inspect the switching apparatus and reset the trailed switch detector.
It is known to have a shunt switch, commonly called a circuit controller switch, positioned to sense movement of the point rail away from the stock rail by a selected distance, at which point the shunt switch will shunt the associated track circuit, indicating that the point rail has moved away from the stock rail. Providing this separate circuit controller switch, possibly calling for an additional housing and connecting apparatus, obviously adds some expense and complexity to the switching arrangement. Further, some currently available switch machines are sufficiently robust that, after a train passes through the switch from the wrong set of diverging tracks, the switch machine will allow the point rail to rebound to a position sufficiently close to the stock rail that the circuit controller switch will immediately open, and the track circuit will no longer be shunted. So, in spite of the added cost of providing the circuit controller switch to detect the trailed switch condition, such known systems do not reliably sense the existence of a trailed switch condition.
Therefore, it is necessary to have apparatus for sensing when a trailed switch condition exists, and to prevent the trailed switch sensing apparatus from resetting itself even if the point rail moves back into contact with its stock rail.